{"id":48276,"date":"2026-10-05T14:35:13","date_gmt":"2026-10-05T14:35:13","guid":{"rendered":"https:\/\/proair.ee\/how-to-heat-a-greenhouse\/"},"modified":"2026-10-05T14:35:13","modified_gmt":"2026-10-05T14:35:13","slug":"how-to-heat-a-greenhouse","status":"publish","type":"post","link":"https:\/\/proair.ee\/en\/how-to-heat-a-greenhouse\/","title":{"rendered":"How to Heat a Greenhouse: Sizing and Equipment Guide"},"content":{"rendered":"\n

For a standard 3 \u00d7 4 m polycarbonate greenhouse in Estonia, a 2\u20133 kW electric fan heater with an integrated thermostat and splash protection (at least IP24)<\/strong> is generally all you need. Tomatoes require a nighttime minimum of 10 \u00b0C to thrive, whereas 4\u20135 \u00b0C is sufficient for basic frost protection. Before investing in a larger heater, seal drafty doors and vents and line the interior walls with bubble wrap\u2014it is the single most cost-effective way to curb heat loss. Never run unvented gas, paraffin, or direct-fired diesel heaters in an enclosed greenhouse: combustion byproducts stunt plant growth and create dangerous conditions for humans.<\/p>\n\n\n\n

\n\n\n\n\n\n\n\n\n
Heating Solution<\/th>\nBest Suited For<\/th>\nMain Drawback<\/th>\n<\/tr>\n<\/thead>\n
Electric fan heater (IP24 or higher)<\/td>\nHobby greenhouses, cold spring nights<\/td>\nOngoing electricity costs; requires an RCD-protected outlet<\/td>\n<\/tr>\n
Infrared panel (IP55)<\/td>\nSeedling benches or targeted zones<\/td>\nLeaves ambient air cool; uneven heat distribution<\/td>\n<\/tr>\n
Indirect-fired diesel heater with flue<\/td>\nLarge commercial greenhouses<\/td>\nSubstantial upfront cost; requires an external exhaust flue<\/td>\n<\/tr>\n
Unvented gas or paraffin heater<\/td>\nNot recommended<\/td>\nEmits ethylene, carbon monoxide (CO), and excess moisture<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/figure>\n\n\n\n

What Temperature to Maintain in a Greenhouse<\/h2>\n\n\n\n

Your target temperature depends entirely on what you are growing. According to the Royal Horticultural Society (RHS), keeping a greenhouse frost-free requires maintaining a nighttime minimum of 4 \u00b0C. Tomatoes do far better when temperatures remain above 10 \u00b0C overnight. The RHS advises holding off on planting cucumbers until nighttime temperatures reliably hold at 12 \u00b0C or higher, while sweet peppers prefer at least 13 \u00b0C.<\/p>\n\n\n\n

Every additional degree of heat significantly increases power consumption, so set your thermostat to the minimum threshold your crops require rather than targeting room temperature. If you are exclusively growing tomatoes, aim for 10\u201312 \u00b0C overnight. If you are simply overwintering pelargoniums or other tender perennials, 5 \u00b0C is plenty.<\/p>\n\n\n\n

In Estonia, supplemental heating is primarily a springtime concern. According to Ilm.ee, the risk of spring frosts generally subsides in early May on the western coast, around May 10\u201315 in Southern Estonia, and from May 20\u201325 in Northern Estonia<\/a>. However, late frosts in Northern Estonia have been documented as late as Midsummer. In unheated greenhouses, growers typically hold off on planting tomatoes until late May, once the soil reaches at least 15 \u00b0C. Adding reliable supplemental heat lets you plant several weeks earlier and harvest well into late autumn.<\/p>\n\n\n\n

How Much Heating Capacity Do You Need?<\/h2>\n\n\n\n

Calculating the heating capacity your greenhouse requires is straightforward: Heat loss (W) = Surface area of covering (m\u00b2) \u00d7 U-value (W\/m\u00b2K) \u00d7 Temperature difference (K)<\/strong>. The U-value measures how many watts of heat escape through one square metre of glazing for each degree of temperature difference between the inside and outside air.<\/p>\n\n\n\n

Typical U-values for dry greenhouse glazing materials:<\/p>\n\n\n\n